Amazonspinther dalmata, a new miniature characid from the streams of rio Purus and rio Madeira, right bank tributaries of the rio Amazonas, is described as a new genus and species of the subfamily Cheirodontinae. The unique characters of the new genus and species are the three remarkable black blotches on the base of the dorsal, anal, and caudal fins, the anteriormost proximal radial of the anal fin with an anteriorly extended lamina entering the abdominal cavity, and the extremely elongate caudal peduncle. The reduced number of ventral procurrent caudal-fin rays (7-9), and the hemal spines of only posterior one, two, or sometimes three caudal vertebrae directly articulating with the ventral procurrent caudal-fin rays further diagnoses the new taxon from remaining genera of the tribe Cheirodontini. The results of a phylogenetic analysis strongly support a close relationship between A. dalmata and Spintherobolus in the tribe Cheirodontini on the basis of fifteen unambiguous synapomorphies. Ten of these characters, previously hypothesized as exclusive synapomorphies for Spintherobolus, were now also identified in Amazonspinther, such as the pattern of exposed neuromasts on the head, the presence of a second pseudotympanum anterior to the first pleural rib, and the nearly discoidal coracoid bone. A discussion about the phylogenetic position of the closely related fossil Megacheirodon to Spintherobolus and Amazonspinther is also provided. Convergent characters shared between Amazonspinther and the characid Priocharax are discussed in relation to miniaturization. Biogeographical implications of the diversification of Amazonspinther, Spintherobolus, and Megacheirodon lineages are discussed.

During an expedition made in 2004 along several southern streams of the rio Amazonas, a new characid species was caught in small streams of the rio Madeira and rio Purus. The fish was promptly recognized as a new species due to three black blotches on the body, unknown in other characid species. Investigation of the phylogenetic relationships of this species allows us to reconstruct sister taxa relationships to Spintherobolus Eigenmann, 1911, of the subfamily Cheirodontinae, a genus phylogenetically diagnosed by Weitzman & Malabarba (1999).

The new genus and species are herein described along with a presentation of a new phylogenetic analysis for the genus Spintherobolus that includes new synapomorphies for the taxon consisting of Spintherobolus and the new genus. Spintherobolus currently contains four species: S. papilliferus Eigenmann, 1911 from the headwaters of rio Tietê, upper rio Paraná basin, and three species distributed in southeastern coastal drainages of Brazil, S. broccae Myers, 1925, S. ankoseion Weitzman & Malabarba, 1999, and S. leptoura Weitzman & Malabarba, 1999. We demonstrate based on a global parsimony analysis of character distribution, that characters shared by the new species and Spintherobolus are homologous and not convergences. We additionally provide a discussion about the implication of the discovery of a closely related Amazonian species concerning evolutionary history of Spintherobolus, in relation to a hypothesis of biogeographical evolution among involved drainages.

Material and Methods

Counts and measurements follow Fink & Weitzman (1974), and were made primarily on the left side of each specimen. Measurements were taken under stereomicroscope with precision of 0.01 mm. Total vertebral number includes the four vertebrae of the Weberian apparatus, and the terminal "half centrum" as outlined by Malabarba & Weitzman (2003). The gill raker at the junction of the ceratobranchial and epibranchial is referred as the posteriormost gill raker of the lower branch of the gill arch, and was included in the count of gill rakers of the lower branch following Bührnheim & Malabarba (2006). Cleared and stained specimens (c&s) were prepared according to Taylor & Van Dyke (1985). Scanning electron micrographs were obtained from first branchial arches of alcohol preserved specimens. Values of meristic traits of the holotype are marked in bold. Values in parentheses along with counts in the description represent number of specimens with the given count. The following institutions provided material for this study: ANSP - Academy of National Sciences of Philadelphia, Philadelphia, USA; INPA - Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil; MCP - Museu de Ciências e Tecnologia, Porto Alegre, Brazil; MNRJ - Museu Nacional, Rio de Janeiro, Brazil; MZUSP - Museu de Zoologia da Universidade de São Paulo, São Paulo, Brazil.

In our discussions, comments about relationships of taxa are based on the concepts of phylogenetic systematics of Hennig (1966). The phylogenetic analysis was performed using TNT 1.0, 2005 by Goloboff, Farris & Nixon (1999), and Winclada 1.00.08, 1999-2002 by Nixon (2002). We used implicit enumeration, the branch and bound algorithm. All characters are given the same weight and are unordered. The matrix of characters includes data from all Spintherobolus species, putatively related cheirodontines, and outgroup characids. Characters 1-35 are numbered following Weitzman & Malabarba (1999), plus nine new characters numbered sequentially (36-44).

Results

Amazonspinther, new genus

Diagnosis.Amazonspinther is diagnosed among all characid species by the autapomorphic presence of three conspicuous black blotches on the base of the dorsal, anal, and caudal fins (ch. 43; Fig. 1).

Amazonspinther is diagnosed among all genera of the Cheirodontinae by two uniquely derived characters, the anteriormost proximal radial of the anal fin with an anteriorly extended lamina entering the abdominal cavity, between the distal portions of the 12th to 14th pleural ribs (ch. 44; Fig. 2) (vs. short anteriorly extended lamina, not entering the abdominal cavity and not between pleural ribs), and by the extremely elongate caudal peduncle, corresponding to 27.3-30.2% of SL. Caudal peduncle length is comparatively short in cheirodontines, ranging from 11.0 to 19.6% of SL. Spintherobolus papilliferus has an elongate caudal peduncle (21.3-27.0% of SL), but shorter than that observed for Amazonspinther.

Etymology. Amazon, in reference to the Amazon basin, and spinther from the Greek spinther, masculine, meaning sparks, fire, in reference to both the closely related genus Spintherobolus and to the appearance of the yellow neuromasts of the head, also observed in Spintherobolus (Fig. 4).

Etymology. The epithet refers to the Portuguese word "dalmata", in allusion to the color pattern of the skin of the dogs of the Dalmatian breed which resembles the color of A. dalmata. The origin of this word is linked to the Dalmatia region currently in Croatia, where the dog breed was possibly developed. A noun in apposition.

Phylogeny of Amazonspinther

A single most parsimonious cladogram (tree length = 53, Consistency Index = 0.88, Retention Index = 0.92) was obtained from the analysis of 44 characters and 8 taxa (Table 2, excluding the fossil Megacheirodon, discussed below). Amazonspinther was found to be closely related to Spintherobolus, and both genera as sister group to Serrapinnus (Fig. 10). Amazonspinther dalmata is a miniature characid according to Weitzman & Vari's (1988) definition. Those authors stated that miniature characid fish species mature sexually at less than 20 mm SL, and are not reported to exceed 25 to 26 mm SL in the wild. Females of A. dalmata are fully mature at a very small size (15.73 mm SL), and the largest known specimen reached less than 20 mm SL. Mature males, however, were not found among the specimens examined.

The current phylogenetic hypothesis available (Malabarba, 1998) for the small sized cheirodontines is strongly based on secondary sexual characters of males, and the lack of mature males of A. dalmata does not allow the examination of thirteen characters potentially informative to access the relationships of A. dalmata with cheirodontines. Nevertheless the new species is found to share several uniquely derived characters with the species of Spintherobolus as defined by Weitzman & Malabarba (1999), supporting a hypothesis of phylogenetic relationship between A. dalmata and the Neotropical Cheirodontinae.

Coding of characters 6, 7, 8, 9, 10, 11, 12, 13, 14, 22, 23, 32 and 37 below depended on the examination of fully mature males. We performed two distinct analyses, one in which all these characters were coded as missing for A. dalmata, and the second with all these characters coded as the outgroup ("0") for A. dalmata. Character 28, the relatively short pectoral-fin was also coded as missing in the latter analysis, because the average percentuals of SL would fit in state 1, but minimum and maximum percentiles of SL would not (Appendix 1). In both analyses, A. dalmata resulted as sister taxon to Spintherobolus (Fig. 10, characters coded as missing). Characters 1 through 35 were extensively described and discussed by Malabarba (1998) and Weitzman & Malabarba (1999), and are presented here in summarized format reporting the respective numeration in those papers (Appendix 1).

Monophyly of Amazonspinther dalmata + Spintherobolus

A close relationship between Amazonspinther dalmata and Spintherobolus is strongly supported by fifteen unambiguous synapomorphies, described below. The first ten characters herein analyzed were more extensively discussed by Malabarba (1998) and Weitzman & Malabarba (1999) as synapomorphies for Spintherobolus, and are herein expanded as synapomorphies of A. dalmata + Spintherobolus.

A complex, patterned series of exposed neuromasts is distributed on the head and body (ch. 69 in Malabarba, 1998: 216, see discussion under ch. 15 in Weitzman & Malabarba, 1999: 12-13, figs. 4, 10 and 11). This is a character shared by A. dalmata and Spintherobolus species. Patterns of exposed neuromasts found in A. dalmata are similar and homologous to those of Spintherobolus (compare Fig. 4 here with Weitzman & Malabarba, 1999: 124, 10).

The dentary has a large anterior fenestra (Fig. 5), associated with a large epidermal, papilla-like structure surrounded by a deep groove that has its deep internal portion lodged in the dentary fenestra. The external surface of this papilla bears several exposed neuromasts. The ventral face of the dentary bone, posterior to the fenestra, is concave (ch. 5 in Malabarba, 1998: 216, and ch. 16 in Weitzman & Malabarba, 1999: 128, fig. 12).

Infraorbital bones are reduced in number and possibly fused. Amazonspinther dalmata has the first and second infraorbitals fused and slightly bifurcated anteriorly, and the third infraorbital reduced (Fig. 11). Fourth to sixth infraorbitals are absent, as observed for Spintherobolus (see discussion under ch. 9 in Malabarba, 1998: 216, and ch. 18 in Weitzman & Malabarba, 1999: 128, fig. 13).

There is a small number of pelvic-fin rays, not exceeding six branched rays (see ch. 14 in Malabarba, 1998: 216, and discussion under ch. 19 in Weitzman & Malabarba, 1999: 129, fig. 14). Amazonspinther dalmata has i,5,i and Spintherobolus species i,4,i; i,5; i,5,i or i,6, while remaining cheirodontines show i,7-8 branched rays.

The anal fin has a small number of 9-16 branched rays. This number varies among the species of this clade, with the highest range observed in S. broccae (13-16 branched rays; state 1), an intermediate range in S. ankoseion and S. leptoura (11-14; state 2), and the smallest number found in A. dalmata and S. papilliferus (8-9 and 9-10, respectively; state 3). State 0 corresponds to 16 to 24 branched rays, following Weitzman & Malabarba (1999: character 20; figs. 9 and 15). Reduction in the number of branched anal-fin rays is a synapomorphy of A. dalmata + Spintherobolus. The remarkably reduced number of branched anal-fin rays in A. dalmata and S. papilliferus is the lowest observed in Cheirodontinae but it is most parsimoniously accepted as basal in the clade Amazonspinther + Spintherobolus.

Lateral line is reduced to 2-6 perforated scales (see ch. 60 in Malabarba, 1998: 216, and discussion under ch. 25 in Weitzman & Malabarba, 1999: 131). Amazonspinther dalmata has 4-5 scales, averaging 4.8, similar to that of S. papilliferus (4.6).

The coracoid bone of the pectoral girdle (Fig. 12) is reduced in length, and more or less discoid in shape (ch. 13 in Malabarba, 1998: 216, and ch. 26 in Weitzman & Malabarba, 1999: 131, fig. 18).

The pectoral-fin is relatively short. Weitzman & Malabarba (1999: 132; ch. 28) found this character to be ambiguous, supporting two equally parsimonious hypotheses: the acquisition in a common ancestor to Spintherobolus and a reversal in S. ankoseion, or the independent acquisition in S. papilliferus and in the clade S. broccae + S. leptoura. The presence of a short pectoral fin in A. dalmata (13.82-16.30 % of SL, mean 15.19) supports this character as a synapomorphy of Amazonspinther + Spintherobolus, and the longer pectoral fin of S. ankoseion as autapomorphic and a reversal.

New characters added herein are as follows:

The teeth are conical to tricuspid (ch. 36, Fig. 5). We treat the conical or tricuspid teeth separately and independent of teeth pedunculation (ch. 3). The conical to tricuspid teeth are proposed as a synapomorphy of A. dalmata + Spintherobolus (vs. multicuspid teeth of remaining cheirodontines - except the compsurin Macropsobrycon uruguayanae).

The antorbital of A. dalmata and Spintherobolus species is short and rounded to oval (ch. 38, Fig. 11), instead of elongate, slender and ventrally expanded, as observed in the remaining Cheirodontinae. It resembles that of Carnegiella, Gasteropelecidae (adnasal in Weitzman, 1954). Not checked in S. leptoura.

The gill rakers are short and conical, instead of elongate and lanceolate (ch. 40, Fig. 6).

The gill rakers on the lower branch of the first gill arch are absent or only the posteriormost gill raker at the junction of the ceratobranchial and the epibranchial is present (ch. 41, Fig. 6). Gill rakers on the lower branch of the first gill arch are always present on remaining cheirodontines. First branchial arches of the four known Spintherobolus species were checked for comparisons with A. dalmata. All the species lack gill rakers or have only one gill raker (the posteri rmost) on lower branchial branch, and the gill rakers are conical and the shortest among cheirodontines (Figs. 6a-d). Amazonspinther dalmata has 3 upper gill rakers and none on the lower branch (two c&s specimens) (Fig. 6a). Spintherobolus papilliferus has none (1), 5(4), 6(6), 7(2) upper gill rakers, and one (13) lower gill raker (the posteriormost). The anteriormost gill rakers on upper branch are very short in the specimen photographed (Fig. 6b). Spintherobolus broccae has 1(2), 2(4) on upper gill rakers, and none (2) or 1(4) lower gill rakers (Fig. 6c). Spintherobolus ankoseion has 1(4), 2(2), 3(2), 4(1), 5(2) upper gill rakers and one (11) lower gill raker (the posteriormost, in photographed specimen not visible, damaged) (Fig. 6d). In contrast, Spintherobolus leptoura has 2-3 upper gill rakers, and one lower gill raker (two alcohol specimens examined). For comparison, Cheirodon ibicuhiensis has 7 gill rakers on upper branch and 11 on lower branch, and Serrapinnus heterodon has 5 on upper branch and 13 on lower branch (Fig. 6e-f).

The maxillary shape is irregular, not bearing a smooth dorsal border. Instead, there are two concave sections in the dorsal border of the maxilla separated by a dorsal short projection in the bearing tooth region of the bone (ch. 42, Fig. 5). The anterior arm of the maxilla that articulates to the premaxilla is thicker than usual in the Characidae. Remaining cheirodontines have a smooth dorsal border in the maxilla.

Monophyly of Spintherobolus

Most characters previously used to diagnose Spintherobolus by either Malabarba (1998) or Weitzman & Malabarba (1999) are herein proposed as synapomorphies of Amazonspinther + Spintherobolus. Two characters remain synapomorphic for Spintherobolus: the lack of an adipose fin (Weitzman & Malabarba, 1999: 131, ch. 17), and the relatively small eye. The eyes of Spintherobolus species are remarkably small compared to that of remaining cheirodontines (see discussion in Weitzman & Malabarba, 1999: 131, ch. 27). Amazonspinther dalmata has large horizontal eye diameter 33.0-39.4% of head length compared to 21.3-28.7% observed in Spintherobolus.

The hypothesis of relationships among Spintherobolus species proposed herein (Fig. 10) agrees with that proposed by Weitzman & Malabarba (1999), in which S. papilliferus is the sister species of one clade formed by the other three species of the genus. Additionally, the polytomy formed by S. broccae, S. leptoura, and S. ankoseion (Weitzman & Malabarba, 1999) was resolved in the present study. The low number of gill rakers on the upper branch of the first gill arch (1-3, ch. 39) supports a hypothesis of sister group relationship between S. broccae and S. leptoura (Fig. 10), a character that independently appears in A. dalmata. The higher number of gill rakers observed in S. ankoseion and S. papilliferus is suggested as plesiomorphic.

Remarks on Amazonspinther apomorphic characters

A high number of ventral procurrent caudal-fin rays (11-28) is a synapomorphy for the Cheirodontini, and the small number (7-9) observed in Amazonspinther (Fig. 3) is a reversal (Malabarba, 1998; Bührnheim, 2006). Similarly, the ventral procurrent caudal-fin rays articulating with the hemal spines of at least the four posterior caudal vertebrae is a synapomorphy of the tribe Cheirodontini, and the reduced articulation observed in Amazonspinther (Fig. 3) is a reversal (Weitzman & Malabarba, 1999: 9, ch. 9; fig. 8).

The phylogenetic position of Megacheirodon unicus

Megacheirodon unicus (Travassos & Santos, 1955) is an extinct cheirodontine, previously proposed as sister-group to Spintherobolus by M. C. Malabarba (1998a,b). The species is known only through two fossilized specimens, a female and a highly sexually dimorphic male. Support for its inclusion in the tribe Cheirodontini is given by the apomorphic traits found in both anal and caudal fins of the male specimen.

The inclusion of the fossil in the analysis and the most parsimonious resulting tree allowed the recognition of Megacheirodon as sister group to Spintherobolus + Amazonspinther (Fig. 13), but we have reservations about these results. Three apomorphic traits are shared by M. unicus and Spintherobolus species and are absent in Amazonspinther, and six synapomorphies are shared by Spintherobolus species and Amazonspinther, and are absent in M. unicus. Sixteen characters, however, are missing in the fossilized remains of this fish (1, 2, 15, 16, 17, 21, 24, 28, 31, 34, 35, 38, 39, 40, 41, and 43). Further complications are related to the lack of mature males of Amazonspinther dalmata that resulted in coding 13 characters as missing in this species (6, 7, 8, 9, 10, 11, 12, 13, 14, 22, 23, 32 and 37). Although monophyly of the Clade Megacheirodon + Spintherobolus + Amazonspinther, seems to be strongly supported, the internal relationships among the three genera may change with the addition of the missing information.

So far, characters supporting a close relationship between Spintherobolus and Amazonspinther and that are absent in Megacheirodon unicus (see M. C. Malabarba, 1998 for characters description in M. unicus) are, infraorbital bones reduced or fused (ch. 18); one unbranched and five or six branched pelvic-fin rays (ch. 19); anal fin with iii unbranched and 8-16 branched rays (ch. 20); lateral line with 2 to 6 perforated scales (ch. 25), the coracoid bone of the pectoral girdle discoid in shape (ch. 26), and the teeth conical or with three cusps (ch. 36).

Two synapomorphies are shared by all Spintherobolus species and Megacheirodon unicus, but these are observed only in mature males, and mature males of A. dalmata were unavailable for comparisons. Both characters, however, are related to the fusion and reduced proximal portion of the anteriormost ventral procurrent caudal-fin rays. Since A. dalmata has a small number of ventral procurrent caudal-fin rays, located posteriorly and in the usual position found in other characids (Fig. 3), we expect the following characters are unlikely to occur in A. dalmata: the anterior ventral procurrent caudal-fin rays in adult males, those that have their proximal ends inserted anterior to the hemal spine of the antepenultimate vertebrae, are proximally fused to one another (Weitzman & Malabarba, 1999: 130, ch. 22; fig. 8); and the anterior ventral procurrent caudal-fin rays of males have reduced proximal portions, not rising above the area of fusion between the rays, while the posterior dorsal portions of these rays are fused into a flat compressed plate that inserts between the hemal spine of the antepenultimate vertebra and the hemal spines of the anterior vertebrae (Weitzman & Malabarba, 1999: 131, ch. 23; fig. 8).

One additional apomorphic trait present in Megacheirodon unicus, clearly discernible in the male specimen (M. C. Malabarba, 1998: 195, fig. 3), is the pterygiophore of the sixth branched anal-fin ray, directed dorsally, away from the fifth which is directed anteriorly and in parallel with the pterygiophores anterior to it (Sarraf, 1997: Fig. 6; Weitzman & Malabarba, 1999: character 33; fig. 9). Such character is shared with S. ankoseion, S. leptoura and S. broccae, again suggesting a close relationship of Megacheirodon unicus to Spintherobolus.

Discussion

The proposal of the new genus Amazonspinther is based on the recognition of a new lineage in the Amazon basin, closely related to a group that succeeded in the coastal drainages of southeastern Brazil. The new species is easily identified by the presence of three conspicuous black blotches on each on the base of the dorsal, anal, and caudal fins, not observed in any other characid. It has two other uniquely derived features among all cheirodontines, the anteriormost proximal radial of the anal fin with an anteriorly extended lamina entering the abdominal cavity, and the extremely elongate caudal peduncle, corresponding to 27.3-30.2% of SL. Two additional characters distinguishes A. dalmata in the inclusive tribe Cheirodontini, the small number of ventral procurrent caudal-fin rays (7-9 vs. 11-28), and the hemal spines of only posterior one, two, or sometimes three caudal vertebrae directly articulating with the ventral procurrent caudal-fin rays. Although the close relationship between A. dalmata and Spintherobolus is supported by fifteen unambiguous synapomorphies, the five apomorphic features of A. dalmata distinguish a stem with an unexpected geographical distribution, the Amazon basin. The biogeographical implications of that are further discussed.

Priocharax and Amazonspinther, a case of convergence associated with miniaturization

The genus Priocharax contains two miniature characin species P. ariel and P. pygmaeus (maximum 17 mm SL), that appear morphologically similar to Amazonspinther dalmata. Priocharax species, however, do not have the synapomorphies of cheirodontines (Malabarba, 1998). According to Weitzman & Vari (1987), the apparent derived and non-paedomorphic characters of numerous conic teeth and elongate maxillae in the genus suggest that its relationships lie in the subfamily Characinae of Géry (1977). Priocharax has or appears to have plesiomorphic character states described in various characines and cynopotamines. Among his studies with characine taxa, Lucena (1998) found a clade that includes most of the suggested Characinae genera by Géry (1977). In this clade Priocharax was found to be a basal sister group of the broader clade composed by Gnathocharax, Hoplocharax, Heterocharax, Lonchogenys, Phenacogaster, Cynopotamus, Acestrocephalus, Galeocharax, Acanthocharax, Charax, and Roeboides.

We have compared the Priocharax and Amazonspinther species and found that the external similarity of these species is due to convergence related to miniaturization. Priocharax species do not share the following synapomorphies described above for Amazonspinther dalmata and Spintherobolus: a complex patterned series of exposed neuromasts on the head and body; the teeth elongate and conical or tricuspid; the dentary bearing a large anterior fenestra; the symphyseal dentary joint surfaces smooth oval articulations lacking the intercalated and folded bony surfaces; the coracoid bone reduced in length, and more or less discoid in shape; the relatively short pectoral-fin length; the anal fin with a reduced number of 9-16 branched rays; the gill rakers on upper branch short and conical; the gill rakers on lower branch of the first gill arch absent or with only the posteriormost gill raker at the junction of the ceratobranchial and the epibranchial; and maxilla shape irregular, not bearing a smooth dorsal border.

Similar to Amazonspinther dalmata and Spintherobolus species, however, Priocharax species show infraorbital bones reduced in number, the antorbital short and rounded to oval, an anterior pseudotympanum anterior to the first pleural rib, low number of pelvic-fin rays, not exceeding six branched rays, and lateral line reduced to 2-6 perforated scales (no pored lateral line scales observed in Priocharax). Similar to Spintherobolus species, Priocharax also lacks an adipose fin. By parsimony, and considering characters grouping Amazonspinther to Spintherobolus and Cheirodontinae and characters grouping Priocharax to Characinae, we consider these characters as convergences related to miniaturization. The reductive nature of the absence of the adipose fin, the body size reduced, absent and possibly fused infraorbitals, low number of branched pelvic-rays, and reduction of the lateral line related to the small size were discussed to Spintherobolus by Weitzman & Malabarba (1999). Other reductive characters related to small size not discussed by Weitzman & Malabarba (1999), but common to Priocharax and to the clade Amazonspinther + Spintherobolus are the absence of laterosensory canals on parietal, frontal, and preopercle, discussed in the small size species of Paracheirodon by Weitzman & Fink (1983).

Malabarba & Lucena (1995) and Malabarba (1998:201) have registered the presence of similar and potentially homologous pseudotympanuns in all species of the Cheirodontinae and in the characine genera Phenacogaster, Charax, Roeboides, and Cynopotamus. Malabarba (1998) also stated that "in the absence of additional synapomorphies supporting the Characinae + Cheirodontinae, or at least the Cheirodontinae plus the group formed by Charax, Roeboides, and Phenacogaster as monophyletic, the pseudotympanums of both groups are considered homoplastic." However, phylogenetic hypotheses based on molecular characters supports a close relationship between taxa of the Characinae and Cheirodontinae taxa such as Cynopotamus + Cheirodon (Ortí & Meyer, 1997), and (Exodon + Roeboides) + ((Aphyocheirodon + Cheirodon) + Cheirodontops + Prodontocharax)) (Calcagnotto et al., 2005), and in this case the pseudotympanum of characines and cheirodontines could be interpreted as homologous and a probable synapomorphy grouping both subfamilies. If so, the external resemblance of the miniature characid of the genera Priocharax and Amazonspinther may be related to their common and not long ancestry among characid fishes.

Biogeographic implications of the discovery of Amazon spinther dalmata

The age of the fossil Megacheirodon unicus given by M. C. Malabarba (1998) allow us to hypothesize a minimum age of 30-25 Myr (Late Oligocene-Early Miocene) to the diversification of Spintherobolus, Amazonspinther, and Megacheirodon lineages, according to the phylogenetic hypothesis presented herein.

Previous hypotheses have supported a sister-group relationship of Serrapinnus, a genus widespread in Amazonian, Paraná-Paraguay, São Francisco and other small drainages, to the clade Spintherobolus + Megacheirodon from coastal drainages of southeastern Brazil. Such pattern of sister group relationships usually at genus level between Atlantic coastal drainages and adjacent continental shields in which both sister-clades underwent subsequent radiation was described by Ribeiro (2006) as "Pattern B" and exemplified with Spintherobolus and a few different lineages of fishes. The discovery of Amazonspinther does not affect the classification of Ribeiro (2006) for Spintherobolus, but changes drastically a pattern of sister group with highly diversified and widespread genus (Serrapinnus) to a so far monotypic and apparently relictual species (Amazonspinther dalmata).

Distribution of Spintherobolus, Amazonspinther, and Megacheirodon lineages seems to demonstrate that the clade formed by them has suffered extensive local extirpation. The modern genus Spintherobolus is represented by four species with very limited and allopatric distributional ranges. Three species are found in small Atlantic coastal drainages from Santa Catarina to Rio de Janeiro States, in Brazil, and Spintherobolus papilliferus, is a rare species occurring in a very restricted area, in the headwaters of the rio Tietê. The last species of this Clade, Amazonspinther dalmata, is found considerably far away from eastern Brazil, into the Amazon basin area. There is, consequently, a large gap in the distribution of that clade, with a large extension of the central portion of South America lacking records of either Amazonspinther or Spintherobolus. It seems feasible to hypothesize a relictual pattern of distribution for the clade that probably underwent a process of extinction through much of its former range. Extinction seems still to be a current process in this Clade. All four Spintherobolus species are listed as critically endangered in Brazil due to their very limited, relictual distributional ranges, in areas subject to high level of anthropogenic disturbances.

Otherwise, the discovery of Amazonspinther dalmata may represent the first of new findings of this clade in the Amazon basin. A great part of Neotropical fish fauna has been recognized in the last decades in an accelerated rate of description of new species (Vari & Malabarba, 1998) and several species remain to be discovered. The limited knowledge of the Brazilian Amazonian ichthyofauna, with a few drainages relatively well surveyed, such as the rio Negro basin (Goulding et al., 1988; Chao, 2001), makes difficult the evaluation of its overall biodiversity, as well as the recognition of priority areas for conservation and sustainable use (Barthem, 2001).

We thank José L. de Figueiredo and Osvaldo Oyakawa (MZUSP) for loaning specimens. Specimens of the new species were caught during the Transcontinental Expedition and supported by the All Catfish Species Inventory (NSF DEB 0315963). Specimens were also acquired through GEOMA project/INPA collections carried out by Jansen Zuanon, Fernando Mendonça (live specimens photo), Helder Espírito Santo, André Galuch and Daniela Barros. We thank their collaboration to this study. SEM micrographs were taken at "Centro de Microscopia e Microanálises" - PUCRS and "Centro de Microscopia Eletrônica" - UFRGS.

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Weitzman, S. H. 1954. The osteology and relationships of the South American characid fishes of the subfamily Gasteropelecinae. Stanford Ichthyological Bulletin, 4(4):213-263. [ Links ]

Weitzman, S. H. & S. V. Fink. 1983. Relationships of the neon tetras, a group of South American freshwater fishes (Teleostei: Characidae), with comments on the phylogeny of the New World characiforms. Bulletin of the Museum of Comparative Zoology, 150(6):339-395. [ Links ]

Weitzman, S. H. & R. P. Vari. 1987. Two new species and a new genus of miniature Characid fishes (Teleostei, Characiformes) from Northern South America. Proceedings of the Biological Society of Washington, 100(3):640-652. [ Links ]

(2) A characteristic hiatus occurs in musculature of the body wall in the area of the swimbladder between the first and second pleural ribs, exposing the swimbladder (Weitzman & Malabarba, 1999: character 2; figs. 4, 5 & 6) (state 1) A hiatus if present involving different muscles and pleural rib limits (state 0).

(3) Teeth have slight proximal peduncle or pedicle and an expanded and compressed distal region bordered by a few to three cusps (state 1). This is different fromWeitzman & Malabarba (1999: character 3; fig. 7) that coded teeth with proximal peduncle or pedicle and an expanded and compressed distal region bordered by a few to many cusps as state 0. Herein teeth not pedunculated, tooth base enlarged (state 0), and teeth pedunculated, largely expanded, and compressed distally (state 2).

(4) A single series of teeth on the premaxilla (Weitzman & Malabarba, 1999: character 4) (state 1). Two tooth rows or different from state 1 (state 0).

(6) The ventral procurrent caudal-fin rays of males are elongate and the ray halves of each side are fused their entire length (Weitzman & Malabarba, 1999: character 6) (state 1). Ventral procurrent caudal-fin rays of males with the ray halves forms a V shape bone in frontal view with its two halves fused only distally (state 0). Tested with state 0 and ? in the matrix.

(7) The anteriormost ventral procurrent caudal-fin rays of the females have the proximal portions of their ray-halves fused to each other, but retain an opening near their distal tips, giving a needle-like shape to these rays (Weitzman & Malabarba, 1999: character 7) (state 1). Females have the entire lengths of their ray halves separate (state 0). Tested with state 0 and ? in the matrix.

(8) Several of the anteriormost ventral procurrent caudal-fin rays of males project through the muscles at which point they are covered only by extremely thin skin, thus they can be easily seen along the ventral margin of the caudal peduncle (Weitzman & Malabarba, 1999: character 8; fig. 8) (state 1). Anterior ventral procurrent caudal-fin rays buried in the muscles and skin and are not visible along the ventral surface of the caudal peduncle in males (state 0). Tested with state 0 and ? in the matrix.

(9) Males have the hemal spines of four or more posterior caudal vertebrae anterior to the terminal "half centrum" and its processes elongated and associated with the ventral procurrent caudal-fin rays support (Weitzman & Malabarba, 1999: character 9; fig. 8) (state 1). Only the posterior one, two, or sometimes three caudal vertebrae directly articulating with the ventral procurrent caudal-fin rays in males (state 0). Tested with state 0 and ? in the matrix.

(10) In males the anterior branched anal-fin rays 1 through 5-8 are slab shaped and five to eight times more expanded in the sagittal plane than comparable rays in the females (Weitzman & Malabarba, 1999: character 10; fig. 9) (state 1). Anal-fin rays in males usually circular in cross section and progressively reduced in diameter from the anteriormost to the most posterior one (state 0). Tested with state 0 and ? in the matrix.

(11) The ray segments of the expanded rays progressively fuse to one another as the male specimens become fully mature (Weitzman & Malabarba, 1999: character 11, fig. 9) (state 1). Ray segmentes not fused (state 0). Tested with state 0 and ? in the matrix.

(12) The proximal ends of the anal-fin rays of males have their lepidotrich bases extended anteriorly (Weitzman & Malabarba, 1999: character 12; fig. 9) (state 1). The proximal ends of the anal-fin rays of males lacking an anterior extension. Tested with state 0 and ? in the matrix.

(13) Adult males with two to four (or sometimes five) anal-fin ray hooks on the posterior border of the hook bearing segments (Weitzman & Malabarba, 1999: character 13) (state 1). Only one or two hooks per segment on the posterolateral border of the anal-fin rays I adult males (state 0). Tested with state 0 and ? in the matrix.

(15) A complex, patterned series of exposed neuromasts are distributed on the head and body (Weitzman & Malabarba, 1999: character 15, figs. 6, 10 & 11) (state 1). Neuromasts not as state 1 (state 0).

(16) The dentary has a large anterior fenestra, associated with a large epidermal, papilla-like structure surrounded by a deep groove that has its deep internal portion lodged in the dentary fenestra. The external surface of this papilla bears several exposed neuromasts. The ventral face of the dentary bone, posterior to the fenestra, is concave (Weitzman & Malabarba, 1999: character 16; fig. 12) (state 1). Dentary lacking an anterior fenestra or with a different fenestra as state 1 (state 0).

(21) An anterior pseudotympanum lies anterior to the first pleural rib (Weitzman & Malabarba, 1999: character 21) (state 1). None anterior pseudotympanum anterior to the first pleural rib or present but involving different muscle and rib limits than those described in state 1 (state 0).

(22) In adult males the anterior ventral procurrent caudal-fin rays, those that have their proximal ends inserted anterior to the hemal spine of the antepenultimate vertebrae, are fused to one another proximally (Weitzman & Malabarba, 1999: character 22; fig. 8) (state 1). Fused elements absent in males (state 0).Tested with state 0 and ? in the matrix.

(23) The anterior ventral procurrent caudal-fin rays of males have reduced proximal portions, not rising above the area of fusion between the rays, while the posterior dorsal portions of these rays are fused into a flat compressed plate that inserts between the hemal spine of the antepenultimate vertebra and the hemal spines of the anterior vertebrae (Weitzman & Malabarba, 1999: character 23; fig. 8) (state 1). Anterior ventral procurrent caudal-fin rays of males not reduced in proximal portions (state 0). Tested with state 0 and ? in the matrix.

(25) Lateral line reduced to 2-6 perforated scales (Weitzman & Malabarba, 1999: character 25) (state 1). Lateral line complete or with higher number of scales than in state 1 (0).

(26) The coracoid bone of the pectoral girdle is reduced in length, and more or less discoid in shape (Weitzman & Malabarba, 1999: character 26; fig 18) (state 1). Elongate coracoids (state 0).

(27) The eyes of Spintherobolus papilliferus (18.4-26.0, in average 21.3 % HL) are the smallest of the four species of Spintherobolus (state 2) (Weitzman & Malabarba, 1999: character 27). Eyes small , S. ankoseion, S. broccae, and S. leptoura, in average 27.2-28.7% HL ( state 1). Relatively large eyes, 25-35 % HL (state 0).

(32) The ray segments of the posterior branch of the second through fifth anal-fin rays of fully adult males are thickened and have a characteristic somewhat asymmetrical chevron shape in lateral profile (Weitzman & Malabarba, 1999: character 32; figs. 9 & 15) (state 1). Ray segments relatively rectangular, either short or elongate, in males (state 0). Tested with state 0 and ? in the matrix.

(33) The pterygiophore of the sixth branched anal-fin ray in both males and females is directed dorsally, away from the fifth which is directed anteriorly and in parallel with the pterygiophores anterior to it (Weitzman & Malabarba, 1999: character 33; fig. 9) (state 1). Anteriorly directed pterygiophores of the branched anal-fin ray in both males and females (state 0).

(34) A black pigmented area lies ventral to the eyes (Weitzman & Malabarba, 1999: character 34; figs. 2, 4, 29-37) (state 1). None black pigmented area ventral to the eyes or different from state 1 (state 0).

(35) A longitudinal stripe occurs on the body dorsal to the anterior lobe of the anal-fin and extends onto the short posterior branched anal-fin rays (Weitzman & Malabarba, 1999: character 35; figs. 2, 29-37) (state 1). None longitudinal stripe as described in state 1 (state 0).

(36) Number of teeth cusps. Conical to tricuspid teeth (state 1). Teeth with four cusps or more (state 0). Amazonspinther dalmata has conical to tricuspid dentary teeth, intermediated by a bicuspid tooth, and unicuspid premaxillary teeth. In Spintherobolus species there are small lateral cusps near the distal apices of what are essentially teeth having an elongate pedicle and a slightly recurved apical cone; see Weitzman & Malabarba, 1999: Fig. 12. The anterior dentary teeth of Spintherobolus have three small cusps. Teeth bearing these small cusps are more numerous than the strictly conical teeth present in the large species, Spintherobolus papilliferus. The premaxillary teeth are usually conical in Spintherobolus species, but in S. papilliferus they bear some very small lateral cusps in their somewhat laterally expanded distal portions. The maxillary teeth in all species, A. dalmata and Spintherobolus species are conical.

(37) Anal-fin rays of males. The last unbranched and about four branched anal-fin rays slab-shaped, including all the branches expanded forming a typical fan (state 1). Different from the state 1 (state 0). This is an autopomorphy Spintherobolus papilliferus, not verified in A. dalmata. Tested with state 0 and ? in the matrix.

(38) Form of antorbital. Short, rounded to oval (state 1). Form different from state 1, elongate, slender, ventrally expanded, in form of a inverse comma in Cheirodontinae (state 0). The Spintherobolus antorbital is relatively similar to that of Carnegiella, Gasteropelecidae (adnasal in Weitzman, 1954). The Gasteropelecidae is a group of uncertain relationships in Characiformes not sharing the synapomorphies of Cheirodontinae (Malabarba, 1998). Not checked in S. leptoura.

(39) Number of gill rakers on upper branch of first gill arch. Low number of gill rakers, 1-3 (state 1). High number gill rakers, 4-7 (or higher in outgroup) (state 0). The higher number of gill rakers observed in S. ankoseion and S. papilliferus is suggested as plesiomorphic. However, this character is variable in S. ankoseion, reaching 4-5 gill rakers, or 1-2 gill rakers. We assume S. ankoseion is plesiomorphic (Character 39, state 0) because some specimens reach a higher number of gill rakers than A. dalmata, S. broccae and S. leptoura, with only none to 3 gill rakers.

(40) Form of gill rakers. Short in a conical form (state 1). Elongate, lanceolate (state 0).

(41) Gill rakers on lower branch of the first gill arch. Absent or with only the posteriormost gill raker at the junction of the ceratobranchial and the epibranchial (state 1). Present (state 0).

(42) Form of maxilla, dorsal profile. Irregular, with a concave protuberance on middle portion of maxilla, above the inferior border with teeth, slightly convex on posteriormost border (state 1). Almost straight, slightly convex on posteriormost border or not (state 0).